The present invention relates to a thermal protector used to prevent danger such as fire caused by an excessive rise in temperature of electrical equipment.
For the thermal protector of this type, water or the like sometimes intrudes into a switching mechanism section thereof depending on the operating environment of equipment to which the thermal protector is applied. Also, when the thermal protector of this type is incorporated in a small-size battery pack, electrolyte leaking from a secondary battery in the battery pack sometimes intrudes into the switching mechanism section. Further, when insulating vanish is used in an assembling process for equipment to which the thermal protector is applied, the insulating vanish sometimes intrude into the switching mechanism section.
The aforementioned entrance of water, electrolyte, vanish, and the like into the switch mechanism section may impair the function of the switching mechanism section. Furthermore, for a lithium ion battery in which the secondary battery of the battery pack uses flammable electrolyte, leaking electrolyte may be ignited by an arc generated at a contact of the switch mechanism.
Therefore, for the thermal protector used for a battery pack or the like, hermetically sealing ability is secured by taking some measures. For example, the switch mechanism section is inserted in a case of a bottomed cylindrical shape, and the opening of the case is sealed by a resin or rubber packing, or an opening between a part prepared by hermetic seal and a metallic case of a bottomed cylindrical shape is welded over the whole circumference.
However, any of the aforementioned measures requires much time and labor in fabrication. Specifically, the measure in which the opening of the case is sealed by a resin requires heating treatment for curing the resin because a liquid resin is used. Also, the measure in which the opening is sealed with a packing requires much time and labor to mount packings one by one. Further, the measure in which hermetic seal is used requires an inspection process for checking the hermetically sealing ability after the welding work over the whole circumference of opening is completed.
Also, any of the aforementioned measures has a problem in that it is difficult to make the whole shape of thermal protector small and thin by using a thin case because the case must have strength.
A method has been used as a trial in which a switch mechanism section is contained in a bottomed case in such a manner that external connection terminals are exposed to the outside, and after a cover is put on the upper opening of the case, the cover is welded to the upper face of the case by ultrasonic welding. However, if the thickness of the cover is decreased to provide a thin shape, the cover cannot withstand vibration energy needed for the ultrasonic welding, and therefore may be damaged.
The present invention has been made in view of the above situation, and accordingly an object thereof is to provide a thermal protector that can provide high hermetically sealing ability with a simple and low-cost construction and also can be of a small and thin shape.
The thermal protector in accordance with the present invention comprises a switching mechanism section having a fixed contact, a movable contact disposed so as to face the fixed contact, and first and second external connection terminals projecting sideward and connected electrically to the fixed contact and movable contact, respectively, the switching mechanism section being constructed so that the movable contact is displaced by a deforming operation of a thermally-actuated element so as to be separated from and brought into contact with the fixed contact; a resin made bottomed case having a peripheral wall located around the switching mechanism section in such a manner that the first and second external connection terminals penetrate the peripheral wall, in which the penetrating portions of the external connection terminals are adhesively sealed by molding the peripheral wall integrally with the connection terminals; and a film-form cover member formed of an electric insulating material, the cover member being adhesively fixed to the upper end face of the peripheral wall of the case so as to seal the upper opening of the case.
According to the present invention, there can be provided a thermal protector that can keep the switching mechanism section in a hermetically sealed state with a simple and low-cost construction.
Also, since a film-form cover member thinner than resin molded products, among the electric insulators certified in the safety standard, is used to seal the opening of the case, the thermal protector can be constructed so as to have a small and thin shape.
Further, since sufficient hermetically sealing ability is insured, the thermal protector can suitably used for a secondary battery pack that has a possibility of leaking electrolyte.
The end face of the peripheral wall of the case is preferably formed so as to be flush to increase the sealing ability of the cover member and further decrease the thickness of the thermal protector.
The outside surface of the cover member is preferably covered with a reinforcing cover plate formed of a thin metallic sheet to increase the mechanical strength for coping with external force. In this case, since the inside surface of the reinforcing cover plate is covered by the cover member, the reinforcing cover plate need not be insulated electrically by an insulating tape or insulating tube.
The switching mechanism section can include a movable plate that is provided with the movable contact at one end portion thereof and is electrically connected to the second external connection terminal at the other end portion thereof. If the thermally-actuated element performs a deforming operation, one end portion of the movable plate is displaced upward, so that the movable contact separates from the fixed contact.
In the switching mechanism section, the movable contact can be provided at one end portion of the thermally-actuated element, and the other end portion of the thermally-actuated element can be electrically connected to the second external connection terminal. If the thermally-actuated element performs a deforming operation, the movable contact is displaced upward, so that the movable contact separates from the fixed contact.
In the case where the switching mechanism section includes the movable plate, the relative positional relationship between the cover member and the switching mechanism section can be set so that when the thermally-actuated element is deformed excessively by abnormal heat generation at the fixed contact and movable contact due to unstable contact or by abnormal heat generation in the movable plate due to an abnormal excessive current, the front end portion of the movable plate comes into contact with the inside surface of the cover member. In this case, the cover member is formed of a resin capable of being melted by the heat at the front end potion of the movable plate being in contact with the inside surface.
According to this construction, if heat is generated abnormally at the fixed contact and movable contact by unstable contact or if heat is generated abnormally in the movable plate by an abnormal excessive current, there can be provided a safety function of maintaining the opened state of the contacts of the switching mechanism section by utilizing the thermally melting properties and adhering properties of the cover member.
In the case where the movable contact is provided on the thermally-actuated element, the relative positional relationship between the cover member and the switching mechanism section can be set so that when the thermally-actuated element is deformed excessively by abnormal heat generation at the fixed contact and movable contact due to unstable contact or by abnormal heat generation in the thermally-actuated element due to an abnormal excessive current, the front end portion of the thermally-actuated element comes into contact with the inside surface of the cover member sealing the upper opening of the case. In this case, the cover member is formed of a resin capable of being melted by the heat at the front end potion of the thermally-actuated element being in contact with the inside surface.
According to this construction, if heat is generated abnormally at the fixed contact and movable contact by unstable contact or if heat is generated abnormally in the thermally-actuated element by an abnormal excessive current, there can be provided a safety function of maintaining the opened state of the contacts of the switching mechanism section by utilizing the thermally melting properties and adhering properties of the cover member.
As the thermally-actuated element, a bimetallic element that performs reversing operation at a predetermined temperature can be used.
Also, as the thermally-actuated element, a shape memory alloy that performs reversing operation at a predetermined temperature can be used.
The cover member can be constructed so that one surface of a film consisting of a thermosetting resin or paper is coated with a thermoplastic resin. The cover member is adhesively fixed to the case by melting the thermoplastic resin with heat.
The cover member can be constructed so that a film consisting of a thermoplastic resin is laminated on one surface of a film consisting of a thermosetting resin. The cover member is adhesively fixed to the case by melting the film consisting of a thermoplastic resin with heat.
The cover member can be constructed so that a film consisting of a thermoplastic resin is lapped over a film consisting of a thermosetting resin or heat resisting paper. The cover member is adhesively fixed to the case by melting the film consisting of a thermoplastic resin with heat.
The cover member can be constructed so that a plurality of films consisting of a thermoplastic resin having different melting points are laminated so that a film having the highest melting point is positioned on the outside. The cover member is adhesively fixed to the case by melting with heat the films except at least the film having the highest melting point.
The cover member can be formed of a heat-sealing film. The cover member is adhesively fixed to the case by heating the heat-sealing film.
The cover member can be formed of an adhesive tape formed by coating a film having heat resistance and electric insulating properties with an adhesive material. The cover member is fixed to the case by the adhesive force of the adhesive material.
The cover member can be formed of a film consisting of a resin having a melting point higher than the melting point of the material for the case and higher than the reversing operation temperature of the thermally-actuated element by a predetermined temperature or more. The cover member is adhesively fixed to the case by melting the end face of peripheral wall of the case with heat.
The thermal protector in accordance with another embodiment of the present invention comprises a switching mechanism section having a fixed contact, a movable contact disposed so as to face the fixed contact, and first and second external connection terminals projecting sideward and connected electrically to the fixed contact and movable contact, respectively, the switching mechanism section being constructed so that the movable contact is displaced by a deforming operation of a thermally-actuated element so as to be separated from and brought into contact with the fixed contact; a resin made bottomless case having a peripheral wall located around the switching mechanism section in such a manner that the first and second external connection terminals penetrate the peripheral wall, in which the penetrating portions of the external connection terminals are adhesively sealed by molding the peripheral wall integrally with the connection terminals; and film-form cover members formed of an electric insulating material, the cover members being adhesively fixed to the upper and lower end faces of the peripheral wall of the case so as to seal the upper and lower openings of the case, respectively.
This thermal protector can provide the same effect as that of the thermal protector having the bottomed case.